He is not sinful, because the Messenger of Allah ﷺ made the apparent indication sufficient to permit the oath.

In matters that men do not normally have access to, such as women’s defects beneath their clothing, virginity and previous marriage, menstruation, childbirth, breastfeeding, a newborn’s cry, and the like, the testimony of one upright woman is accepted. A man’s testimony in such matters is equivalent to a woman’s. Whoever brings one man and two women, or one witness together with an oath, in a case entailing retaliation, establishes neither retaliation nor financial liability thereby. If he produces such evidence in a theft case, the property is established but not the prescribed amputation. If he produces it in a khulʿ case, the compensation is established for him, and the separation is established merely by his claim.

His statement, “In matters that men do not normally have access to,” means: in most cases, since men may sometimes become aware of the matters he mentioned. However, women are generally the ones who have access to these matters. The word “what” is a relative pronoun, whose predicate is the phrase, “the testimony of one upright woman is accepted.”

His statement, “such as women’s defects beneath their clothing,” refers to conditions such as leprosy and the like. Defects beneath women’s clothing are generally known only to women. Therefore, if a woman testifies that the wife whom a man has married has leprosy beneath her clothing, it is ruled to be established. The husband then has the right to annul the marriage, and he may recover the dower from the one who deceived him, as mentioned previously.

His statement, “virginity and previous marriage,” means that a dispute may arise between husband and wife as to whether she is a virgin or has previously been married. If a woman testifies that virginity is present, her testimony in this matter is accepted, because this is generally known only to women. Likewise, if she testifies that the woman has previously been married, her testimony is accepted, because this is generally known only to women. Thus, if the wife claims that her husband is unable to have intercourse, and the husband says that he is able and has in fact had intercourse, a woman is brought to examine the wife. If she finds her to have previously been married, we rule that she has been sexually penetrated. The converse is likewise true: if the man claims that the woman is not a virgin, having stipulated that she be a virgin, and she says that she is indeed a virgin, then she brings a woman to testify, and we accept her testimony.

His statement, “and menstruation”: menstruation is generally known only to women,